1. Field of the Invention
The present invention relates to a method of coloring a magnesium material to be used for making the housing of a portable device such as a notebook computer. The present invention also relates to a housing made of such a colored magnesium material. The “magnesium material” in this specification refers to both pure metal magnesium and a magnesium alloy.
2. Description of the Related Art
Recently, the housings of mobile electronic devices such as notebook computers and cellular phones are often made of a magnesium material, so that the electronic products are compact and light. The housing made of a magnesium material is also advantageous to causing the heat generated by the inside components (e.g. the CPU, MPU, etc.) to efficiently dissipate. As known, a magnesium material is an easily oxidizable metal. Thus, to be used for making a housing, the magnesium material is subjected to surface treatment to be resistible against corrosion.
One of the known anticorrosive techniques is chemical conversion treatment, whereby a magnesium material is immersed in chemicals to develop a coating film on the material surface. The conversion treatment utilizes chemical reaction that occurs voluntarily. Thus, it is difficult to control the process and hence the thickness of the coating film. Another problem is that the resultant coating film often fails to grow to be thick enough to exhibit appropriate resistance against corrosion.
Anodic treatment, or anodizing, is preferable to the above conversion treatment in forming a thicker coating film. JP-A-11(1999)-256394, for example, discloses an anodizing technique for an aluminum material, which can be applied for anodizing a magnesium material. By the conventional anodic treatment, however, the oxide film formed on the magnesium material is rather dark or sober. Unfavorably, this may deteriorate the appearance of the finished product.
To decorate the magnesium material of the above-described kind, an organic paint, which is less influenced by the dark color of the oxide film, needs to be applied to the oxide film. The organic paint, however, generates toxic gas when it is burnt. To avoid this, the organic paint film needs to be removed with a solvent or by wet blasting in the recycling process. However, the removing of the paint film deteriorates the working conditions and increases the number of the steps to be performed. Further, the organic paint film tends to peel off the material surface due to the deterioration of the film quality, which is not desirable for good appearance of the product.